To analyze changes in cardiac output and hemodynamic volumes using transpulmonary ultrasound dilution (TPUD) in a neonatal animal model under different hemodynamic conditions. 7 lambs (3.5-8.3 kg) under general anesthesia received arterial and central venous catheters. A Gore-Tex((R)) shunt was surgically inserted between the descending aorta and the left pulmonary artery to mimic a patent ductus arteriosus. After shunt opening and closure, induced hemorrhagic hypotension (by repetitive blood withdrawals) and repetitive volume challenges, the following parameters were assessed using TPUD: cardiac output, active circulating volume index (ACVI), central blood volume index (CBVI) and total end-diastolic volume index (TEDVI). 27 measurement sessions were analyzed. After shunt opening, there was a significant increase in TEDVI and a significant decrease in cardiac output with minimal change in CBVI and ACVI. With shunt closure, these results reversed. After progressive hemorrhage, cardiac output and all volumes decreased significantly, except for ACVI. Following repetitive volume resuscitation, cardiac output increased and all hemodynamic volumes increased significantly. Correlations between changes in COufp and changes in hemodynamic volumes (ACVI 0.83; CBVI 0.84 and TEDVI 0.78 respectively) were (slightly) better than between changes in COufp and changes in heart rate (0.44) and central venous pressure (0.7). Changes in hemodynamic volumes using TPUD were as expected under different conditions. Hemodynamic volumetry using TPUD might be a promising technique that has the potential to improve the assessment and interpretation of the hemodynamic status in critically ill newborns and children.